1. Field
The presently disclosed subject matter relates to a fluorescent lamp, and more particularly to a hot cathode fluorescent lamp which, in at least one embodiment, can be used as a light source for a lighting unit such as a back light unit of a liquid crystal display mounted in a casing.
2. Description of the Related Art
Fluorescent lamps are broadly used as a light source in various fields such as a general lighting, consumer products, industrial products, etc. The fluorescent lamps can be generally classified into a cold cathode fluorescent lamp (CCFL) and a hot cathode fluorescent lamp (HCFL) type lamp.
The CCFL is frequently used as a light source for a backlight unit, which is mounted on the back of a liquid crystal display (LCD) in order to facilitate visualization of the LCD while using office automation equipment such as a personal computer, a printer, etc. A reason why the CCFL is frequently used as a light source for the backlight unit is that the CCFL may not generate a large amount of heat and may enjoy low power consumption. The HCFL also comes into use as a light source for the backlight unit in equipment using a large size LCD, because it has characteristics of both a high luminescent efficiency type lamp and high-light intensity lamp as compared with the CCFL.
Typical fluorescent lamps can include: a tube unit coated with a phosphor on an inner surface thereof; a couple of stems, each attached to a respective end of the tube unit so as to seal the tube therebetween, the stems can each include an electrode so that each electrode faces with respect to each other in the tube unit; and a filler gas including a mercury vapor and an inert gas can be enclosed in the tube unit. In this case, the CCFL can emit a discharge optical light without heating the electrodes thereof and the HCFL can emit a discharge optical light by heating the electrodes thereof.
The luminescent efficiency of the fluorescent lamp may be changed by the vapor pressure of mercury in the filler gas that is enclosed in the tube unit. The vapor pressure of mercury may be adjusted so as to become a maximum value of the luminescent efficiency at around 25 degrees centigrade of ambient temperature in which the fluorescent lamp may be used. The vapor pressure may be easily varied with changes in temperature of a coolest point in the tube unit.
Therefore, various arts for properly maintaining the vapor pressure are generally known. For example, Patent Document No. 1 (Japanese Patent No. 3478369) discloses a fluorescent lamp including a structure for providing a coolest portion with an edge portion of an exhaust pipe, and therefore the conventional fluorescent lamp may prevent the coolest portion from experiencing a significant or undesired rise in temperature thereof. Patent Document No. 2 (Japanese Patent Application Laid Open JP2001-243875) discloses a fluorescent lamp that provides cooling holes with an edge portion for mounting the circular fluorescent lamp in order to prevent the coolest portion from experiencing a significant or undesired rise in temperature.
On the other hand, a fluorescent lamp for allowing a charge optical emission at a high ambient temperature is disclosed in Patent Document No. 3 (Japanese Patent Application Laid Open H10-12191). The conventional fluorescent lamp provides a mercury amalgam with a coolest portion that is located at an edge portion thereof. Therefore, the conventional fluorescent lamp may prevent the mercury from over-evaporating under the circumstance of a high ambient temperature.
The above-referenced Patent Documents are listed below, and are hereby incorporated with their English abstracts in their entireties.    1. Patent Document No. 1: Japanese Patent No. 3478369    2. Patent Document No. 2: Japanese Patent Application Laid Open JP2001-243875    3. Patent Document No. 3: Japanese Patent Application Laid Open H10-12191
When the fluorescent lamp is used as a light source for a lighting unit such as a backlight unit, the bulb-typed lighting unit may be sealed within an outer casing or the like, and the fluorescent lamp may be left in a space in which an ambient temperature may easily rise because of heat generated from the lamp or from the control circuit. Therefore, luminescent efficiency of the fluorescent lamp may decrease because vapor pressure of mercury within the lamp becomes higher than its usual pressure.
In this case, in the conventional fluorescent lamps which provide a coolest portion, the coolest portion is integrated with the tube unit or the stem using the same material such as a glass, a ceramic, and the like, and is formed with a low radiating structure especially in the casing. Therefore, the conventional fluorescent lamp may not prevent the coolest portion from experiencing a rise in temperature with confidence under the above-described circumstance in which the ambient temperature thereof easily rises, and the rise in temperature near the coolest portion may cause an increase of the vapor pressure of mercury.
Thus, the conventional fluorescent lamp may experience a negative effect such that the luminescent efficiency may easily decrease, especially under the above-described circumstance. The fluorescent lamp may require that an effective radiator be provided with the coolest portion thereof in order to consistently prevent the coolest portion from experiencing the above-described rise in temperature. However, the fluorescent lamp including the radiator requires a more complex structure for manufacture, a higher relative cost, etc.
With respect to the conventional fluorescent lamp including the mercury amalgam, it may be difficult to quickly evaporate the mercury at the beginning of emission for the fluorescent lamp, and the vapor pressure of mercury may become low. Therefore, the fluorescent lamp may include a negative effect in that the light intensity thereof may become low at the beginning of emission. In addition, because an impurity may become easily attached to a surface of the mercury amalgam, the fluorescent lamp may cause a problem in that the vapor pressure of mercury may venture outside of a predetermined appropriate value.
The disclosed subject matter has been devised to consider the above and other features, problems and characteristics. Thus, embodiments of the disclosed subject matter can include a fluorescent lamp with a simple structure that can prevent the coolest portion from a rise in temperature and can prevent the lamp from experiencing a decrease of luminescent efficiency even under the circumstance in which the ambient temperature may rise. The disclosed subject matter can also include a lighting unit using the fluorescent lamp, which can maintain a favorable light-emission even in a sealed casing.